125. Gynogenesis in fishes is achieved by:
1. Heat shock treatment at 42°C for 5 min after normal fertilization.
2. Cold shock treatment at 5°C for 10 min after normal fertilization.
3. Fertilization of egg with UV-irradiated sperm followed by heat shock treatment.
4. Treatment of fertilized eggs with cytochalasin.
What is Gynogenesis in Fishes?
Gynogenesis is a type of asexual reproduction in fishes, where the development of the embryo occurs without genetic contribution from the sperm. Although sperm is used to activate the egg, the paternal DNA does not participate in forming the zygote. This results in offspring that are genetically identical to the mother.
Correct Answer: 3. Fertilization of egg with UV-irradiated sperm followed by heat shock treatment
How Gynogenesis is Induced
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Sperm Irradiation:
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Sperm is exposed to ultraviolet (UV) light, which damages the DNA without affecting its ability to activate the egg.
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This prevents the paternal genome from being expressed in the embryo.
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Activation and Chromosome Doubling:
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The egg is fertilized with the UV-irradiated sperm.
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Immediately after fertilization, the zygote is subjected to heat shock treatment, usually around 42°C for a short duration.
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This heat shock inhibits the second polar body extrusion or suppresses first mitotic division, leading to the retention of diploidy from the maternal chromosomes.
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Applications of Gynogenesis
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Production of all-female fish stocks (in species with XX-female sex determination)
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Clonal line development for genetic studies
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Conservation of endangered species
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Aquaculture breeding programs for consistent traits
Why Not the Other Options?
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Option 1 & 2: Heat or cold shock alone cannot induce gynogenesis unless combined with UV-treated sperm.
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Option 4: Cytochalasin B affects cytokinesis and is more commonly used in triploidy induction, not specifically gynogenesis.
Conclusion
Gynogenesis is a powerful tool in fish genetics and aquaculture. By using UV-irradiated sperm followed by heat shock treatment, researchers and breeders can manipulate reproduction to produce genetically uniform offspring, opening new avenues in genetic improvement and species conservation.
